There has been known a Shack-Hartmann sensor as a method for measuring wavefront aberration. For example, there is an explanation as a representative case of a wavefront measuring sensor in Tsuruta, Tadao, Pencil of Rays Vol. 4, Singijutsu Communications, 1997, p. 212.
In an optical system of a wavefront aberration measuring apparatus for measuring wavefront aberration generated in a test lens, an illumination optical system that illuminates the test lens with a bundle of rays and a measuring optical system that measures wavefront aberration of the bundle of rays are generally used.
In the measuring optical system, upon analyzing wavefront aberration generated by the test lens, a shape of a projected aperture has to be known. Accordingly, an aperture stop of the test lens is projected to be measured the shape thereof. In this instance, in order to derive the center of the aperture stop, the shape and the position of the aperture stop may be measured with fully stopping down the aperture stop.